Numerical Analysis of Thermal Performance of Flat-Plate Solar Air–Water Heater for Simultaneous Heating of Air and Water

A solar air–water heater (SAWH) is a solar collector capable of heating air and water simultaneously. Although many studies have examined the performance and applicability of SAWHs, the effects of operating conditions, weather conditions, and design parameters on their thermal behavior remain unclear. In this study, the thermal behavior of an SAWH operating in simultaneous air-heating and water-heating mode was investigated under various conditions. A numerical model based on energy balance equations was developed and validated against experimental data. The validated model was then used to determine the effects of inlet air and water temperatures, air and water mass flow rates, weather conditions, fin height, and number of fins. The air-side and water-side thermal efficiencies ranged from −18.2% to 83.19% and from −14.58% to 98.87%, respectively, which indicates that improper operating conditions may cause heat loss. The total thermal efficiency ranged from 63.37% to 85.81%. Among the investigated parameters, the inlet fluid temperature, air mass flow rate, solar irradiance, and fin height considerably influenced thermal efficiency, whereas the effects of the other parameters were relatively limited. These findings are expected to provide valuable guidance for predicting SAWH performance and selecting appropriate operating and design conditions, thereby promoting the wider adoption and application of this type of solar collector.